A guide to streaming SSR with React 18

React 18 introduces significant enhancements to server-side rendering (SSR), particularly with the addition of streaming features that address previous performance and user experience limitations. The SSR process involves the server rendering the React application to HTML, which is then sent to the client for display. Before React 18, SSR faced challenges such as the need for complete data fetching before rendering and a monolithic transmission of HTML to the client, which hindered performance and interactivity. React 18 overcomes these issues with features like the Suspense component and the renderToPipeableStream API, enabling incremental rendering and streaming of HTML content. This allows for a more efficient flow where data-fetching and rendering can be synchronized, and HTML can be transmitted in chunks rather than as a single block. Additionally, the introduction of ReactDOMClient.hydrateRoot facilitates selective hydration on the client side, allowing parts of the application to be hydrated independently based on priority and user interaction, thus enhancing responsiveness and reducing loading times. These changes collectively improve the scalability and performance of SSR in React applications, marking a significant evolution from previous versions.